Proximity fuse



July 31, 1962 c. cossE ETAL 3,046,892

PROXIMITY FUSE Filed June l8, 1959 3 Sheets-Sheet 1 INVENT0R5 CLAUDE sass: PERM ND LOY BY a AGENT July 31, 1962 Filed June 18, 1959 2 V Q I C. COSSE ETAL PROXIMITY FUSE I5 Sheets-Sheet 2 INVENTORfi CLAUDE 60335 FERNfiND L OY July 31, 1962 c. COSSE ETAL PROXIMITY FUSE 3 Sheets-Sheet 3 Filed June 18, 1959 FIG. 3

INVENTORS CLAUDE 60555 FERNAND LOY AGEN United S tates Patent Ofiiice 3,46,8Z Patented July 31, 1962 3,046,892 PROXMITY FUSE Claude Cosse, Paris, and Fernand Loy, Neuilly-snr=Seine,

France, assignors to Telecommunications Radioelectriques et Telephoniques, T.R.T. (Societe Anonyme),

Paris, France Filed June 18, 1959, Ser. No. 821,259 Claims priority, application France June 20, 1958 3 Claims. (Cl. 102-701) This invention relates to proximity fuses for detonating the load of a projectile as soon as it has approached a target up to a predetermined distance.

It has been found that not only the distance, but also the angular position of the target with respect to the flight of the proximity fuse are important. In order to'obtain an optimum effect, the aim will be that the detonation does not take place until the target is in a zone which is described when a sector, with its apex approximately at the area of the peak of the projectile, turns about the axis of the fuse. Usually the requirement is made that this sector shall have a comparatively small angle of aperture of, for example, a few degrees. Even when use is made of aerials having a sharp directional effect, it is difiicult with radio systems to fulfil the said requirement.

The use of an aerial wherein the main loop of the direction diagram is very narrow, does not prevent errors still occurring as a result of detection on a secondary loop and it is usually difficult to adjust beforehand the angle at which the projectile approaches its target.

The present invention relates to a device of the kind mentioned in the preamble, in which by means of radio waves a signal is obtained if a target is at a distance which is less than a predetermined distance.

An object of the invention is to provide such a device which permits of adjusting the position of the target with respect to the axis of the fuse at the moment of detonation with high accuracy.

The invention consists in that, in combination with the said radio-electric means, use is made of optical means producing a signal at a given angular position, but only if a target is present in a portionof the space determined by an angle, provision being made of a coincidence device so that detonation can occur only if both signals are present at the same time.

In order that the invention may be readily carried into effect, it will now be described in detail, by way of example with reference to the accompanying drawing, in which:

FIG. 1a shows a longitudinal section of the optical part of a device according to the invention;

FIG. 1b is a cross-sectional view of this device;

FIG. 2 shows the diagram of a device according to the invention;

FIG. 3 shows a projectile provided with a device according to the invention, and

FIG. 4 is a cross-sectional view of the peak of a projectile having a device according to the invention, in which the relative positioning of the various elements is shown.

In a device according to the invention, in order to be struck with reasonable security, the target must be present in a zone determined by the optical device and, in order to ensure safe operation there is also provided a radio-electric device which permits detonation onlywhen a target is present within a predetermined distance.

An exact active Zone independent of the surface of the target is defined by means of the optical device,'the field of which may have a very fiat shape; The disadvantages of optical systems are largely eliminated due to their range of activity being limited by means of the radio-electric device.

Interference as a result of the sunlight, clouds, rain and other targets which might be present in the optical field, is eliminated by the requirement that the distance must be less than a predetermined value.

Detonation occurs if the conditions are fulfilled that a target is present within an active zone and that the distance is less than a predetermined critical distance.

The probability of the optical system being interfered, although small, yet exists. .However, the chance of an optical device and the radio-electric device being disturbed simultaneously is very small.

In the device according to the invention, which will be described hereinafter, the optical device is of the passive type, that is to say, a source of radiation is not available. In the day-time the device is sensitive to the contrast between the sky and the aircraft passing through the detection cone determined by the optical device. At night and by day it is sensitive to the infrared radiation of an aircraft passing through the said cone.

In order that the invention may be readily carried into effect, it will now be described in detail by way of example with reference to the accompanying drawing.

In FIGS. 1a and lb, the optical part of a device according to the invention is shown in two sections. Reference numeral 1 indicates the outer wall of the proximity fuse, 2 indicates a photo-electric detector and 3 indicates an annular lens. By means of channels 8, 9, 10, 11 and lens 3, the beams of a conical space the axis of which coincides with the axis of the proximity fuse, are projected onto detector 2. Each channel has two plane mirrors positioned so that, for each window, the incident beam corresponds to a quadrant of the space. Thus, channel It) has two plane mirrors 10a and 1017 on two opposing lateral faces. FIGS. 1a and lb show the paths of the light rays which pass through the channel 10 and are convergent on detector 2. In the embodiment under consideration, the detection cone has an apical angle of about 40, the beam having an angle of aperture of 4. The axis of the channels are inclined at an angle of 40 with respect to the axis of the fuse, their cross-section being 4X4 sq. cms. One embodiment of the device is such that the inclination of the beam with respect to the axis of the fuse may be varied within comparatively wide limits by displacing the detector 2 on the said axis along line AB. In order to obtain the optimum effect, it is alternatively possible for the inclination of the beam to be adapted to the manner in which the projectile approaches its target. The photo-electric detector is contituted by a lead-sulphide cell, the sensitive layer of which is maintained at a temperature below 20 C. One thus obtains, after filtration, a detection in the band between 1 p and 2.7 IL. The windows 4, 5, 6 and 7 are in this case of quartz.

An aircraft, the smallest lateral dimension of which is of the order of 2 metres, at its most unfavorable position occupies 6 of field at a distance of 20 metres and hence, the sixtieth part of the total field of the detector. It may be assumed that, in the day-time, the brightness of the aircraft differs not more than 10% from the brightness ofthe sky so that, when the aircraft passes through the detection cone, thereoccurs avariation of about j of the total amount of light received. This variation can readily be observed if it is more than 10- watts. In fact, use is made of a cell which in the dark can detect 10- watts.

At night, use ismade of the same photo-electric detecting element. For a reactor of 50 cnis. in diameter, the temperature of which is 400 K., it may be calculated that the aircraft sends an amount of energy of 5 X 10- watts to the detector if it is at the most unfavorable angle and at a distance of 20 metres from the optical system under consideration. In the backward direction it sends an amount of energy of l.3 lwatts.

Consideration of the energetic brightness diagrams of the actual aircraft confirms, that, apart from a zone of 10 at the front of the aircraft, this energy may readily be observed when using the lead sulphide cell. It is to be noted thatgif the projectile is directed directly towards the aircraft, the device becomes operative due to the impact. At a reactor temperature of 600 K., the energy received at the most unfavorable position is 5 l0 watts, which may readily be observed with the cell employed.

FIG. 2 shows a diagram of a device according to the invention. A rectangle represents the optical portion and a rectangle represents the radio-electric portion. The former comprises an optical system 21 and the detector 2 previously described, together with an amplifier 23. The latter comprises transistors of the type CC '70; the amplification is 10,000 with a band width of from 500 to 1000 c./s. The radio-electric portion includes a distance meter in which use is made of the Doppler effect and the microphony of oscillators is partly eliminated. An'

aerial 31 serves both for transmission and reception. It is directed forwards and the amplification is 3 db. Reference numeral 32 indicates an oscillator. Any variation in the impedance of the aerial or, which amounts to the same, any energy absorbed by the aerial, results in a variation in the output current of the oscillator. This variation constitutes the useful signal. Along a conductor 33 connecting oscillator 32 and aerial 31, there are arranged two detectors 34 and 35 at a mutual distance of a quarter of a wave-length as measured along theconnection 33. The detectors are arranged at points which, in the absence of a target in the field of the distance meter, correspond to a maximum and a minimum of the voltage of the standing waves which occur as a result of the interference of the waves propagating from the oscillator towards the aerial with the waves which are reflected at the lower end of the aerial and travel from the aerial towards the oscillator. By means of a transformer 36, the primary winding of whichis powered via the oppositely-connected detectors Hand 35 it is possible to setup a voltage at a secondary winding of the transformer, which voltage is proportional to the variable part of the useful signal. The ratio of transmission of the transformer is such that the voltage of the said signal and the input voltage of amplifier 37 are matched with each other. In the embodiments under consideration, thetransformation ratio was 30, the oscillator frequency was 240 mc./s., and the symmetrical mixing system including the two detectors yielded an uncoupling of 30 db;

The signals which, due to their presence, indicate a target at a distance less than 20 metres, are given off by the amplifier 37 in the form of rectangular voltages, whereasthe amplifier 23 indicates the signals which, in the presence of a target occur, in the optical detection :one in the form of a direct voltage located above a given .evel. These various signals are led to a coincidence ievice 40, the output voltage of which controls the detonaion of the projectile by means of a device 41. The coin- :idencedevice '40 may contain a plurality of diodes. The levice 41 contains a thyratron, the anode current of vhich brings about the ignition.

FIG. 3 shows a device E, wherein H represents the 'adiation diagram of the aerial and-F indicates the detecion' cone for the optical device. It is to be noted that the 'adiation diagram of the aerial may be wider than in :nown devices i'n-whichthe directional effect of the aerial mly is used for obtaining an accurate detection ofv angle. The coincidence device controls the detonation if the utput voltage of the optical device indicates the presence 4 of a target in the detection cone-and the output voltage of the radio-electric device indicates the presence thereof at a distance less than 20 metres.

Although the targets brought to light need, strictly speaking, not be the same, it is highly improbable that several targets are indicated by the two detectors at the same time. This applies more particularly if the device is not adjusted until it has left the earth or at least its nose is directed upwards.

In the electrical portion of the device, use may be advantageously made of transistors. The devices, except of course, the aerial may then readily be arranged in a space having a volume of a cubic decimetre. The optical portion may readily be housed in a space which is smaller than 4 cubic decimetres.

FIG. 4 shows in what manner the optical portion and the electrical portion may be positioned with respect to each other. and 10 of the optical detection device and also the photo sensitive detector 2 and the aerials 31 of the radio-electric detector. Two aerials are present so that the desired directional eifect in the forward direction is obtained. The circuits associated with the radio-electric device are housed in a space 30 Whereas the amplifier 23 associated with the optical detector and the coincidence device 40 are arranged in a space 40'.

The optical device may be of the active type, that is to say, may contain a source of radiation, together with'a detector which is sensitive to the radiation reflected by a target.

What is claimed is:

1. A proximity fuse for detonating the charge of a projectile, comprising a source of radio signals, means for transmitting said radio signals, means for receiving said radio signals to provide a first output signal 'dependent upon the proximity of a target, optical means for providing a second output signal dependent upon the occurrence of a target at'a predetermined angular position with respect to the longitudinal axis of said projectile, a coincidence device, means applying said first'and second output signals to said'coincidence device whereby a detonating signal is produced only when said first and second signals both indicate the presence of a target.

2. The fuse of claim 1, wherein said optical means comprises photo-electric detector means, and means'fop directing light rays upon said detector means which originate from light sources located between two concentric cones of revolution whose axes coincidewith the longi tudinal axis of said projectile.

3. A proximity fuse for detonating the charge of a projectile, comprising a source of radio signals, means for transmitting said radio signals, means for receiving said radio signals to provide a first output signal depend ent upon the proximity of a target, photosensitive means, means for directing light from a predetermined angular direction with respect to the longitudinal axis 'of'said projectile on said photosensitive means to provide a second output signal dependent upon the occurrence/of a target in the path of said light, a coincidencedevice' means applying said first and second output signals to said coincidence device whereby a detonating signal ,is produced only when said'first and second signals' both indicate the presence of a target.

References Cited in the file of this patent UNITED STATES PATENTS In this figure may be seen the channels 8' 

